The present invention relates to ultra high temperature plasma gas reactions with various metal compositions to form extremely hard surfaces.
During the past twenty years, considerable work has been done in the development of systems to create plasma, the term generally used to describe a highly energized disassociated gas or mixture of gases. The two most common plasma systems are the consumable electrode system (transferred and non-transferred) and the induction system (no consumables).
Plasma generators for generating such plasma gas typically use an electric arc or an induction coil as a means of utilizing electrical energy to heat the plasma-forming or work gas. In a typical non-transferred arc unit, the work gas flows through the arc passing between the anode and cathode and emerges from the plasma generator as a highly heated gaseous stream or flame. In an induction-type plasma generator, a high frequency induction coil, such as that used in conventional induction heating of metals, surrounds an insulated cylinder of suitable construction through which the work gas is flowed.
A considerable amount of work in this area has been carried out initially with a Thermal Dynamics F-40 plasma torch containing a cathode-anode, non-transferred arc configuration. For the purposes of the present invention, however, the electric arc system was discarded in favor of an induction plasma system. This was done for the following reasons: (1) the induction plasma system does not utilize consumable electrodes and thus does not contaminate the reactive gases; (2) consumable electrodes cause power surges which make the reaction difficult to control; (3) the non-transferred arc system has a limited plasma diameter and relatively high exit velocity in the reaction area; (4) the induction system can use almost any gas to form a plasma since it does not contain reactive electrodes. The advantage of such use is seen in the fact that air may be employed, for example, a substance which would result in rapid oxidization of a tungsten or copper electrode. This feature also provides many possible gasmetal reactions; and (5) the induction system can operate at very low velocities (40 feet per second,) so that the reaction surface is not disturbed or dimensionally changed.
Accordingly, it is an object of the present invention to provide a process which will rapidly convert various metals or metal surfaces so that they possess unique chemical and physical properties.
Another object of the present invention is to provide metal surface hardnesses up to or above Rockwell hardness values of Rc 80, by reacting a plasma gas such as a nitrogen-propane mixture with a saw or razor blade coated with titanium.
Another object of the present invention is to provide excellent corrosion resistance by reactions such as the above titanium-nitrogen-propane system. By treatment in accordance with the present invention, meat saw blades, which are subject to corrosive meat juices, are provided with greatly enhanced corrosion resistance.
A further object of the present invention is to provide a process for treating specific areas of metal objects such as saw blade tooth tips, while the adjacent or substrate areas remain unaffected.
A further object of the present invention is to provide a great variety of possible surface treatments to arrive at the desired metallurgical or chemical properties.
The above and other objects are achieved by the method of the present invention, which includes passing the surface of a cutting tool, such as a saw blade or a razor blade, in contact with plasma gas generated by an induction plasma system. The method includes the insulating of the various metallic components of the treating apparatus, in order to prevent arcing which has been found to occur with induction plasma in an environment of the type described herein. The present method also includes stabilizing of the plasma prior to use in treating the cutting tool surfaces. The present invention allows the use of high speed feeding of the tools for treatment by the plasma, with speeds of up to 150 feet per minute being commonly obtained. During treatment in accordance with the present invention, the surface of the metal is subjected to heat by the plasma to a temperature of from 7,500.degree. to 50,000.degree.F.